1. Field of the Invention
This invention relates in general to integral recording head milliactuators, and more particularly, to a milliactuator with integrated sensor and driver electronics and a process for making the same.
2. Description of Related Art
Moving magnetic storage devices, especially magnetic disk drives, are the memory device of choice. This is due to their expanded non-volatile memory storage capability together with a relatively low cost. Accurate retrieval of the stored information from these devices becomes critical, requiring the magnetic transducer to be positioned as close to the storage media as possible. In some storage devices, the transducer may actually contact the media.
Magnetic disk drives are information storage devices which utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a read/write transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer adjacent the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or a write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air bearing, generated by the rotating disk.
Alternatively, the transducer may operate in contact with the surface of the disk. Thus the suspension provides desired slider loading and dimensional stability between the slider and an actuator arm which couples the transducer/slider/suspension assembly to the actuator. The suspension is required to maintain the transducer and the slider adjacent the data surface of the disk with as low a loading force as possible. The actuator positions the transducer over the correct track according to the data desired on a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled by a servo to position the transducer over the desired data track by shifting the combination assembly across the surface of the disk in a direction generally transverse to the data tracks. A disk drive servo control system controls movement of the actuator arm across the surface of the disk to move the magnetic recording head from data track to data track, once over a selected track, to maintain the head in a path over the centerline of the selected track. Maintaining the head centered over a track facilitates accurate reading and recording of data in the track.
A trend in magnetic disk drives is that the magnetic bit size which may be reliably written and read by the magnetic recording head continues to decrease at a rate around 50% per year. As a consequence, the width of the track which contains the sequential bits must also diminish at roughly half this rate. Thus, an advanced storage device having 4000 to 6000 tracks per inch (tpi) today is likely to have 20 to 25 ktpi within a few years. This projected increase in data density places extreme requirements on the precision with which the actuator system brings the recording head to the data track and maintains the head over the track. The offset between the actual head position and the track center, called the track mis-registration (TMR), scales as the width of the track (approximately 12% of the track-to-track pitch).
As the track density increases and the allowable TMR decreases, the speed or servo bandwidth with which the head positioning servo system can respond must also increase to allow effective track following. One method of increasing this bandwidth is the use of a second actuator (a milliactuator) to provide rapid, small-motion, position correction of the recording head. In this concept, the usual actuator provides coarse position control, and the milliactuator located at the individual head provides fine control of head position over the selected track. In order to achieve high track density, these milliactuators must have a range of motion on the order of a few track pitches and a force output that can impart 10 to 30 G acceleration to the recording head. For the integrated milliactuator/head designs the mass involved is the mass of the slider plus the mass of the movable part of the milliactuator, totaling a few milligrams. A piggyback electrostatic milliactuator positioned between a suspension flexure and a recording head can achieve the positional accuracy and high speed performance required in future high track density applications. Such an electrostatic milliactuator needs high drive voltages and capacitive position sensing signals for good servo control.
A problem with positioning the milliactuator between the suspension flexure and the recording slider is that the drive signal and the capacitive sense signal need to travel through wiring on the suspension. The readback signal and the write current signal also travel through wires placed on the suspension in close proximity to the milliactuator wires. The wiring between the milliactuator and the drive/sense integrated circuit chip adds parasitic load and introduces interferences to the readback signal.
It therefore can be seen that there is a need for a method for reducing or eliminating the interaction and interference between milliactuator drive and control signals and the recording head readback signal.